This invention relates to gas turbine engine exhaust devices and, more particularly, to a simplified actuation system for simultaneously controlling the geometry of multiple concentric exhaust nozzles, and a method of actuating same.
Exhaust systems are provided to direct the exhaust gases rearwardly from a gas turbine engine and into the atmosphere at a velocity and density necessary to produce the required thrust. The advent of new variable mission aircraft has spurred the development of new variable cycle propulsion systems capable of ultra-efficient operation at more than one operating condition. One of the particularly significant objectives of these so-called "variable cycle" gas turbine engines is the desire to maintain high airflow rates through the engine even at relatively low power settings. Typically, airflow varies with thrust. However, in the variable cycle engine, if airflow is maintained as power is decreased two advantages will result. First, air which would normally be "spilled" around the engine inlet will now be captured, thus reducing inlet drag. Secondly, since the exhaust nozzle must be opened to reduce thrust, afterbody drag is reduced.
Furthermore, the performance of any exhaust nozzle is dictated, to a large extent, by its internal geometry which is dictated by the exhaust gas aerodynamic parameters. When the operating range of a gas turbine engine is relatively narrow and the aerodynamic parameters such as pressure, temperature and velocity are relatively constant, the internal geometry may be optimized at the time of manufacture since any performance benefits obtained by providing a variable geometry capability are offset by increased weight, complexity and cost. By definition, however, contemplated variable cycle engines of the future will have wide operating ranges and large excursions in aerodynamic parameters. The requirements of high airflow at low thrust, and considerations of performance, noise and economics will dictate the necessity of variable geometry exhaust nozzles in variable cycle engines.
Some of the more attractive variable cycle gas turbine engines have several coaxial exhaust streams and a similar number of exhaust nozzles. Each nozzle must be actuated in cooperation and in coordination with the other nozzle to optimize the engine performance over the entire operating cycle. The problem confronting the industry is to develop a single actuation system which can simultaneously control such multiple concentric nozzles over this wide range of operation. This will result in savings of weight, complexity and cost.